A good site with lots of pictures and links to many other sites, including "phone diagrams" (text-only descriptions that you could read/hear on the telephone).
Amazing modular origami, where you basically fold a "piece" multiple times, then put all the pieces together to create an awesomely complex-looking 3D origami module.
Modular (3D) and regular origami diagrams. The site isn't in English, but the images are sufficient for advanced origami folders. Definitely check out the molecules and cubes.